[WIP] Inject commands for Minecraft 1.13+

build.gradle

@@ -33,9 +33,16 @@ allprojects {
     repositories {
         mavenLocal()
         mavenCentral()
+        
+        // for kyoripowered dependencies
         maven {
             url 'https://oss.sonatype.org/content/groups/public/'
         }
+        
+        // Brigadier
+        maven {
+            url "https://libraries.minecraft.net"
+        }
     }
 
     test {

proxy/build.gradle

@@ -47,6 +47,8 @@ dependencies {
     compile 'it.unimi.dsi:fastutil:8.2.1'
     compile 'net.kyori:event-method-asm:3.0.0'
 
+    compile 'com.mojang:brigadier:1.0.15'
+
     testCompile "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
     testCompile "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
 }

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommandManager.java

@@ -2,6 +2,7 @@ package com.velocitypowered.proxy.command;
 
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import com.velocitypowered.api.command.Command;
 import com.velocitypowered.api.command.CommandManager;
 import com.velocitypowered.api.command.CommandSource;
@@ -11,6 +12,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 import org.checkerframework.checker.nullness.qual.NonNull;
 
 public class VelocityCommandManager implements CommandManager {
@@ -68,6 +70,10 @@ public class VelocityCommandManager implements CommandManager {
     return commands.containsKey(command);
   }
 
+  public Set<String> getAllRegisteredCommands() {
+    return ImmutableSet.copyOf(commands.keySet());
+  }
+
   /**
    * Offer suggestions to fill in the command.
    * @param source the source for the command
@@ -116,4 +122,31 @@ public class VelocityCommandManager implements CommandManager {
           "Unable to invoke suggestions for command " + alias + " for " + source, e);
     }
   }
+
+  public boolean hasPermission(CommandSource source, String cmdLine) {
+    Preconditions.checkNotNull(source, "source");
+    Preconditions.checkNotNull(cmdLine, "cmdLine");
+
+    String[] split = cmdLine.split(" ", -1);
+    if (split.length == 0) {
+      // No command available.
+      return false;
+    }
+
+    String alias = split[0];
+    @SuppressWarnings("nullness")
+    String[] actualArgs = Arrays.copyOfRange(split, 1, split.length);
+    Command command = commands.get(alias.toLowerCase(Locale.ENGLISH));
+    if (command == null) {
+      // No such command.
+      return false;
+    }
+
+    try {
+      return command.hasPermission(source, actualArgs);
+    } catch (Exception e) {
+      throw new RuntimeException(
+          "Unable to invoke suggestions for command " + alias + " for " + source, e);
+    }
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftSessionHandler.java

@@ -1,6 +1,7 @@
 package com.velocitypowered.proxy.connection;
 
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
+import com.velocitypowered.proxy.protocol.packet.AvailableCommands;
 import com.velocitypowered.proxy.protocol.packet.BossBar;
 import com.velocitypowered.proxy.protocol.packet.Chat;
 import com.velocitypowered.proxy.protocol.packet.ClientSettings;
@@ -67,6 +68,10 @@ public interface MinecraftSessionHandler {
 
   }
 
+  default boolean handle(AvailableCommands commands) {
+    return false;
+  }
+
   default boolean handle(BossBar packet) {
     return false;
   }

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -1,5 +1,9 @@
 package com.velocitypowered.proxy.connection.backend;
 
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.builder.RequiredArgumentBuilder;
+import com.mojang.brigadier.tree.LiteralCommandNode;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.api.network.ProtocolVersion;
@@ -10,6 +14,8 @@ import com.velocitypowered.proxy.connection.client.ClientPlaySessionHandler;
 import com.velocitypowered.proxy.connection.forge.legacy.LegacyForgeConstants;
 import com.velocitypowered.proxy.connection.util.ConnectionMessages;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
+import com.velocitypowered.proxy.protocol.packet.AvailableCommands;
+import com.velocitypowered.proxy.protocol.packet.AvailableCommands.ProtocolSuggestionProvider;
 import com.velocitypowered.proxy.protocol.packet.BossBar;
 import com.velocitypowered.proxy.protocol.packet.Disconnect;
 import com.velocitypowered.proxy.protocol.packet.JoinGame;
@@ -128,6 +134,25 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
     return false; //Forward packet to player
   }
 
+  @Override
+  public boolean handle(AvailableCommands commands) {
+    // Inject commands from the proxy.
+    for (String command : server.getCommandManager().getAllRegisteredCommands()) {
+      if (!server.getCommandManager().hasPermission(serverConn.getPlayer(), command)) {
+        continue;
+      }
+
+      LiteralCommandNode<Object> root = LiteralArgumentBuilder.literal(command)
+          .then(RequiredArgumentBuilder.argument("args", StringArgumentType.greedyString())
+              .suggests(new ProtocolSuggestionProvider("minecraft:ask_server"))
+              .build())
+          .executes((ctx) -> 0)
+          .build();
+      commands.getRootNode().addChild(root);
+    }
+    return false;
+  }
+
   @Override
   public void handleGeneric(MinecraftPacket packet) {
     serverConn.getPlayer().getConnection().write(packet);

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -1,5 +1,7 @@
 package com.velocitypowered.proxy.connection.client;
 
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_13;
+
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
 import com.velocitypowered.api.event.player.PlayerChatEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
@@ -19,6 +21,7 @@ import com.velocitypowered.proxy.protocol.packet.PluginMessage;
 import com.velocitypowered.proxy.protocol.packet.Respawn;
 import com.velocitypowered.proxy.protocol.packet.TabCompleteRequest;
 import com.velocitypowered.proxy.protocol.packet.TabCompleteResponse;
+import com.velocitypowered.proxy.protocol.packet.TabCompleteResponse.Offer;
 import com.velocitypowered.proxy.protocol.packet.TitlePacket;
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import com.velocitypowered.proxy.util.ThrowableUtils;
@@ -133,23 +136,39 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
   @Override
   public boolean handle(TabCompleteRequest packet) {
     // Record the request so that the outstanding request can be augmented later.
-    if (!packet.isAssumeCommand() && packet.getCommand().startsWith("/")) {
-      int spacePos = packet.getCommand().indexOf(' ');
-      if (spacePos > 0) {
-        String cmd = packet.getCommand().substring(1, spacePos);
-        if (server.getCommandManager().hasCommand(cmd)) {
-          List<String> suggestions = server.getCommandManager()
-              .offerSuggestions(player, packet.getCommand().substring(1));
-          if (!suggestions.isEmpty()) {
-            TabCompleteResponse resp = new TabCompleteResponse();
-            resp.getOffers().addAll(suggestions);
-            player.getConnection().write(resp);
-            return true;
+    boolean is113 = player.getProtocolVersion().compareTo(MINECRAFT_1_13) >= 0;
+    boolean isCommand = is113 || (!packet.isAssumeCommand() && packet.getCommand().startsWith("/"));
+
+    if (!isCommand) {
+      // Outstanding tab completes are recorded for use with 1.12 clients and below to provide
+      // tab list completion support for command names. In 1.13, Brigadier handles everything for
+      // us.
+      outstandingTabComplete = packet;
+      return false;
+    }
+
+    int spacePos = packet.getCommand().indexOf(' ');
+    if (spacePos > 0) {
+      String command = is113 ? packet.getCommand() : packet.getCommand().substring(1);
+      String commandLabel = command.substring(0, spacePos);
+      if (server.getCommandManager().hasCommand(commandLabel)) {
+        List<String> suggestions = server.getCommandManager().offerSuggestions(player, command);
+        if (!suggestions.isEmpty()) {
+          List<Offer> offers = new ArrayList<>();
+          for (String suggestion : suggestions) {
+            offers.add(new Offer(suggestion, null));
           }
+          TabCompleteResponse resp = new TabCompleteResponse();
+          resp.setTransactionId(packet.getTransactionId());
+          resp.setStart(spacePos);
+          resp.setLength(command.length() - spacePos);
+          resp.getOffers().addAll(offers);
+          player.getConnection().write(resp);
+          return true;
         }
       }
     }
-    outstandingTabComplete = packet;
+
     return false;
   }
 
@@ -323,7 +342,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
     // Tell the server about this client's plugin message channels.
     ProtocolVersion serverVersion = serverMc.getProtocolVersion();
     Collection<String> toRegister = new HashSet<>(knownChannels);
-    if (serverVersion.compareTo(ProtocolVersion.MINECRAFT_1_13) >= 0) {
+    if (serverVersion.compareTo(MINECRAFT_1_13) >= 0) {
       toRegister.addAll(server.getChannelRegistrar().getModernChannelIds());
     } else {
       toRegister.addAll(server.getChannelRegistrar().getIdsForLegacyConnections());
@@ -362,7 +381,11 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
           && outstandingTabComplete.getCommand().startsWith("/")) {
         String command = outstandingTabComplete.getCommand().substring(1);
         try {
-          response.getOffers().addAll(server.getCommandManager().offerSuggestions(player, command));
+          List<String> offers = server.getCommandManager().offerSuggestions(player, command);
+          for (String offer : offers) {
+            response.getOffers().add(new Offer(offer, null));
+          }
+          response.getOffers().sort(null);
         } catch (Exception e) {
           logger.error("Unable to provide tab list completions for {} for command '{}'",
               player.getUsername(),

proxy/src/main/java/com/velocitypowered/proxy/protocol/ProtocolUtils.java

@@ -109,6 +109,22 @@ public enum ProtocolUtils {
     buf.writeBytes(array);
   }
 
+  public static int[] readIntegerArray(ByteBuf buf) {
+    int len = readVarInt(buf);
+    int[] array = new int[len];
+    for (int i = 0; i < len; i++) {
+      array[i] = readVarInt(buf);
+    }
+    return array;
+  }
+
+  public static void writeIntegerArray(ByteBuf buf, int[] array) {
+    writeVarInt(buf, array.length);
+    for (int i : array) {
+      writeVarInt(buf, i);
+    }
+  }
+
   public static UUID readUuid(ByteBuf buf) {
     long msb = buf.readLong();
     long lsb = buf.readLong();

proxy/src/main/java/com/velocitypowered/proxy/protocol/StateRegistry.java

@@ -19,6 +19,7 @@ import static com.velocitypowered.proxy.protocol.ProtocolUtils.Direction;
 
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.proxy.protocol.packet.AvailableCommands;
 import com.velocitypowered.proxy.protocol.packet.BossBar;
 import com.velocitypowered.proxy.protocol.packet.Chat;
 import com.velocitypowered.proxy.protocol.packet.ClientSettings;
@@ -83,7 +84,8 @@ public enum StateRegistry {
           map(0x14, MINECRAFT_1_8, false),
           map(0x01, MINECRAFT_1_9, false),
           map(0x02, MINECRAFT_1_12, false),
-          map(0x01, MINECRAFT_1_12_1, false));
+          map(0x01, MINECRAFT_1_12_1, false),
+          map(0x05, MINECRAFT_1_13, false));
       serverbound.register(Chat.class, Chat::new,
           map(0x01, MINECRAFT_1_8, false),
           map(0x02, MINECRAFT_1_9, false),
@@ -121,7 +123,10 @@ public enum StateRegistry {
       clientbound.register(TabCompleteResponse.class, TabCompleteResponse::new,
           map(0x3A, MINECRAFT_1_8, false),
           map(0x0E, MINECRAFT_1_9, false),
-          map(0x0E, MINECRAFT_1_12, false));
+          map(0x0E, MINECRAFT_1_12, false),
+          map(0x10, MINECRAFT_1_13, false));
+      clientbound.register(AvailableCommands.class, AvailableCommands::new,
+          map(0x11, MINECRAFT_1_13, false));
       clientbound.register(PluginMessage.class, PluginMessage::new,
           map(0x3F, MINECRAFT_1_8, false),
           map(0x18, MINECRAFT_1_9, false),

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/AvailableCommands.java

@@ -0,0 +1,320 @@
+package com.velocitypowered.proxy.protocol.packet;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.collect.ImmutableList;
+import com.mojang.brigadier.Command;
+import com.mojang.brigadier.arguments.ArgumentType;
+import com.mojang.brigadier.builder.ArgumentBuilder;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.builder.RequiredArgumentBuilder;
+import com.mojang.brigadier.context.CommandContext;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.suggestion.SuggestionProvider;
+import com.mojang.brigadier.suggestion.Suggestions;
+import com.mojang.brigadier.suggestion.SuggestionsBuilder;
+import com.mojang.brigadier.tree.ArgumentCommandNode;
+import com.mojang.brigadier.tree.CommandNode;
+import com.mojang.brigadier.tree.LiteralCommandNode;
+import com.mojang.brigadier.tree.RootCommandNode;
+import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
+import com.velocitypowered.proxy.protocol.MinecraftPacket;
+import com.velocitypowered.proxy.protocol.ProtocolUtils;
+import com.velocitypowered.proxy.protocol.ProtocolUtils.Direction;
+import com.velocitypowered.proxy.protocol.packet.brigadier.ArgumentPropertyRegistry;
+import io.netty.buffer.ByteBuf;
+import it.unimi.dsi.fastutil.objects.Object2IntLinkedOpenHashMap;
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Queue;
+import java.util.concurrent.CompletableFuture;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public class AvailableCommands implements MinecraftPacket {
+  private static final byte NODE_TYPE_ROOT = 0x00;
+  private static final byte NODE_TYPE_LITERAL = 0x01;
+  private static final byte NODE_TYPE_ARGUMENT = 0x02;
+
+  private static final byte FLAG_NODE_TYPE = 0x03;
+  private static final byte FLAG_EXECUTABLE = 0x04;
+  private static final byte FLAG_IS_REDIRECT = 0x08;
+  private static final byte FLAG_HAS_SUGGESTIONS = 0x10;
+
+  // Note: Velocity doesn't use Brigadier for command handling. This may change in Velocity 2.0.0.
+  @MonotonicNonNull
+  private RootCommandNode<Object> rootNode;
+
+  public RootCommandNode<Object> getRootNode() {
+    if (rootNode == null) {
+      throw new IllegalStateException("Packet not yet deserialized");
+    }
+    return rootNode;
+  }
+
+  @Override
+  public void decode(ByteBuf buf, Direction direction, ProtocolVersion protocolVersion) {
+    int commands = ProtocolUtils.readVarInt(buf);
+    WireNode[] wireNodes = new WireNode[commands];
+    for (int i = 0; i < commands; i++) {
+      WireNode node = deserializeNode(buf, i);
+      wireNodes[i] = node;
+    }
+
+    // Iterate over the deserialized nodes and attempt to form a graph. We also resolve any cycles
+    // that exist.
+    Queue<WireNode> nodeQueue = new ArrayDeque<>(Arrays.asList(wireNodes));
+    while (!nodeQueue.isEmpty()) {
+      boolean cycling = false;
+
+      for (Iterator<WireNode> it = nodeQueue.iterator(); it.hasNext(); ) {
+        WireNode node = it.next();
+        if (node.toNode(wireNodes)) {
+          cycling = true;
+          it.remove();
+        }
+      }
+
+      if (!cycling) {
+        // Uh-oh. We can't cycle. This is bad.
+        throw new IllegalStateException("Stopped cycling; the root node can't be built.");
+      }
+    }
+
+    int rootIdx = ProtocolUtils.readVarInt(buf);
+    rootNode = (RootCommandNode<Object>) wireNodes[rootIdx].built;
+  }
+
+  @Override
+  public void encode(ByteBuf buf, Direction direction, ProtocolVersion protocolVersion) {
+    // Assign all the children an index.
+    Deque<CommandNode<Object>> childrenQueue = new ArrayDeque<>(ImmutableList.of(rootNode));
+    Object2IntMap<CommandNode<Object>> idMappings = new Object2IntLinkedOpenHashMap<>();
+    while (!childrenQueue.isEmpty()) {
+      CommandNode<Object> child = childrenQueue.poll();
+      if (!idMappings.containsKey(child)) {
+        idMappings.put(child, idMappings.size());
+        childrenQueue.addAll(child.getChildren());
+      }
+    }
+
+    // Now serialize the children
+    ProtocolUtils.writeVarInt(buf, idMappings.size());
+    for (CommandNode<Object> child : idMappings.keySet()) {
+      serializeNode(child, buf, idMappings);
+    }
+    ProtocolUtils.writeVarInt(buf, idMappings.getInt(rootNode));
+  }
+
+  private static void serializeNode(CommandNode<Object> node, ByteBuf buf,
+      Object2IntMap<CommandNode<Object>> idMappings) {
+    byte flags = 0;
+    if (node.getRedirect() != null) {
+      flags |= FLAG_IS_REDIRECT;
+    }
+    if (node.getCommand() != null) {
+      flags |= FLAG_EXECUTABLE;
+    }
+
+    if (node instanceof RootCommandNode<?>) {
+      flags |= NODE_TYPE_ROOT;
+    } else if (node instanceof LiteralCommandNode<?>) {
+      flags |= NODE_TYPE_LITERAL;
+    } else if (node instanceof ArgumentCommandNode<?, ?>) {
+      flags |= NODE_TYPE_ARGUMENT;
+      if (((ArgumentCommandNode) node).getCustomSuggestions() != null) {
+        flags |= FLAG_HAS_SUGGESTIONS;
+      }
+    } else {
+      throw new IllegalArgumentException("Unknown node type " + node.getClass().getName());
+    }
+
+    buf.writeByte(flags);
+    ProtocolUtils.writeVarInt(buf, node.getChildren().size());
+    for (CommandNode<Object> child : node.getChildren()) {
+      ProtocolUtils.writeVarInt(buf, idMappings.getInt(child));
+    }
+    if (node.getRedirect() != null) {
+      ProtocolUtils.writeVarInt(buf, idMappings.getInt(node.getRedirect()));
+    }
+
+    if (node instanceof ArgumentCommandNode<?, ?>) {
+      ProtocolUtils.writeString(buf, node.getName());
+      ArgumentPropertyRegistry.serialize(buf, ((ArgumentCommandNode) node).getType());
+
+      if (((ArgumentCommandNode) node).getCustomSuggestions() != null) {
+        // The unchecked cast is required, but it is not particularly relevant because we check for
+        // a more specific type later. (Even then, we only pull out one field.)
+        @SuppressWarnings("unchecked")
+        SuggestionProvider<Object> provider = ((ArgumentCommandNode) node).getCustomSuggestions();
+
+        if (!(provider instanceof ProtocolSuggestionProvider)) {
+          throw new IllegalArgumentException("Suggestion provider " + provider.getClass().getName()
+            + " is not valid.");
+        }
+
+        ProtocolUtils.writeString(buf, ((ProtocolSuggestionProvider) provider).name);
+      }
+    } else if (node instanceof LiteralCommandNode<?>) {
+      ProtocolUtils.writeString(buf, node.getName());
+    }
+  }
+
+  @Override
+  public boolean handle(MinecraftSessionHandler handler) {
+    return handler.handle(this);
+  }
+
+  private static WireNode deserializeNode(ByteBuf buf, int idx) {
+    byte flags = buf.readByte();
+    int[] children = ProtocolUtils.readIntegerArray(buf);
+    int redirectTo = -1;
+    if ((flags & FLAG_IS_REDIRECT) > 0) {
+      redirectTo = ProtocolUtils.readVarInt(buf);
+    }
+
+    switch (flags & FLAG_NODE_TYPE) {
+      case NODE_TYPE_ROOT:
+        return new WireNode(idx, flags, children, redirectTo, null);
+      case NODE_TYPE_LITERAL:
+        return new WireNode(idx, flags, children, redirectTo, LiteralArgumentBuilder
+            .literal(ProtocolUtils.readString(buf)));
+      case NODE_TYPE_ARGUMENT:
+        String name = ProtocolUtils.readString(buf);
+        ArgumentType<?> argumentType = ArgumentPropertyRegistry.deserialize(buf);
+
+        RequiredArgumentBuilder<Object, ?> argumentBuilder = RequiredArgumentBuilder
+            .argument(name, argumentType);
+        if ((flags & FLAG_HAS_SUGGESTIONS) != 0) {
+          argumentBuilder.suggests(new ProtocolSuggestionProvider(ProtocolUtils.readString(buf)));
+        }
+
+        return new WireNode(idx, flags, children, redirectTo, argumentBuilder);
+      default:
+        throw new IllegalArgumentException("Unknown node type " + (flags & FLAG_NODE_TYPE));
+    }
+  }
+
+  private static class WireNode {
+    private final int idx;
+    private final byte flags;
+    private final int[] children;
+    private final int redirectTo;
+    @Nullable
+    private final ArgumentBuilder<Object, ?> args;
+    @MonotonicNonNull
+    private CommandNode<Object> built;
+
+    private WireNode(int idx, byte flags, int[] children, int redirectTo,
+        @Nullable ArgumentBuilder<Object, ?> args) {
+      this.idx = idx;
+      this.flags = flags;
+      this.children = children;
+      this.redirectTo = redirectTo;
+      this.args = args;
+    }
+
+    public boolean toNode(WireNode[] wireNodes) {
+      if (this.built == null) {
+        // Ensure all children exist. Note that we delay checking if the node has been built yet;
+        // that needs to come after this node is built.
+        for (int child : children) {
+          if (child >= wireNodes.length) {
+            throw new IllegalStateException("Node points to non-existent index " + redirectTo);
+          }
+        }
+
+        int type = flags & FLAG_NODE_TYPE;
+        if (type == NODE_TYPE_ROOT) {
+          this.built = new RootCommandNode<>();
+        } else {
+          if (args == null) {
+            throw new IllegalStateException("Non-root node without args builder!");
+          }
+
+          // Add any redirects
+          if (redirectTo != -1) {
+            if (redirectTo >= wireNodes.length) {
+              throw new IllegalStateException("Node points to non-existent index " + redirectTo);
+            }
+
+            if (wireNodes[redirectTo].built != null) {
+              args.redirect(wireNodes[redirectTo].built);
+            } else {
+              // Redirect node does not yet exist
+              return false;
+            }
+          }
+
+          // If executable, add a dummy command
+          if ((flags & FLAG_EXECUTABLE) != 0) {
+            args.executes((Command<Object>) context -> 0);
+          }
+
+          this.built = args.build();
+        }
+      }
+
+      for (int child : children) {
+        if (wireNodes[child].built == null) {
+          // The child is not yet deserialized. The node can't be built now.
+          return false;
+        }
+      }
+
+      // Associate children with nodes
+      for (int child : children) {
+        CommandNode<Object> childNode = wireNodes[child].built;
+        if (!(childNode instanceof RootCommandNode)) {
+          built.addChild(childNode);
+        }
+      }
+
+      return true;
+    }
+
+    @Override
+    public String toString() {
+      MoreObjects.ToStringHelper helper = MoreObjects.toStringHelper(this)
+          .add("idx", idx)
+          .add("flags", flags)
+          .add("children", children)
+          .add("redirectTo", redirectTo);
+
+      if (args != null) {
+        if (args instanceof LiteralArgumentBuilder) {
+          helper.add("argsLabel", ((LiteralArgumentBuilder) args).getLiteral());
+        } else if (args instanceof RequiredArgumentBuilder) {
+          helper.add("argsName", ((RequiredArgumentBuilder) args).getName());
+        }
+      }
+
+      return helper.toString();
+    }
+  }
+
+  /**
+   * A placeholder {@link SuggestionProvider} used internally to preserve the suggestion provider
+   * name.
+   */
+  public static class ProtocolSuggestionProvider implements SuggestionProvider<Object> {
+
+    private final String name;
+
+    public ProtocolSuggestionProvider(String name) {
+      this.name = name;
+    }
+
+    @Override
+    public CompletableFuture<Suggestions> getSuggestions(CommandContext<Object> context,
+        SuggestionsBuilder builder) throws CommandSyntaxException {
+      return builder.buildFuture();
+    }
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/TabCompleteRequest.java

@@ -1,5 +1,9 @@
 package com.velocitypowered.proxy.protocol.packet;
 
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_13;
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_9;
+
+import com.google.common.base.MoreObjects;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
@@ -10,6 +14,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 public class TabCompleteRequest implements MinecraftPacket {
 
   private @Nullable String command;
+  private int transactionId;
   private boolean assumeCommand;
   private boolean hasPosition;
   private long position;
@@ -49,25 +54,39 @@ public class TabCompleteRequest implements MinecraftPacket {
     this.position = position;
   }
 
+  public int getTransactionId() {
+    return transactionId;
+  }
+
+  public void setTransactionId(int transactionId) {
+    this.transactionId = transactionId;
+  }
+
   @Override
   public String toString() {
-    return "TabCompleteRequest{"
-        + "command='" + command + '\''
-        + ", assumeCommand=" + assumeCommand
-        + ", hasPosition=" + hasPosition
-        + ", position=" + position
-        + '}';
+    return MoreObjects.toStringHelper(this)
+        .add("command", command)
+        .add("transactionId", transactionId)
+        .add("assumeCommand", assumeCommand)
+        .add("hasPosition", hasPosition)
+        .add("position", position)
+        .toString();
   }
 
   @Override
   public void decode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion version) {
-    this.command = ProtocolUtils.readString(buf);
-    if (version.compareTo(ProtocolVersion.MINECRAFT_1_9) >= 0) {
-      this.assumeCommand = buf.readBoolean();
-    }
-    this.hasPosition = buf.readBoolean();
-    if (hasPosition) {
-      this.position = buf.readLong();
+    if (version.compareTo(MINECRAFT_1_13) >= 0) {
+      this.transactionId = ProtocolUtils.readVarInt(buf);
+      this.command = ProtocolUtils.readString(buf);
+    } else {
+      this.command = ProtocolUtils.readString(buf);
+      if (version.compareTo(MINECRAFT_1_9) >= 0) {
+        this.assumeCommand = buf.readBoolean();
+      }
+      this.hasPosition = buf.readBoolean();
+      if (hasPosition) {
+        this.position = buf.readLong();
+      }
     }
   }
 
@@ -76,13 +95,19 @@ public class TabCompleteRequest implements MinecraftPacket {
     if (command == null) {
       throw new IllegalStateException("Command is not specified");
     }
-    ProtocolUtils.writeString(buf, command);
-    if (version.compareTo(ProtocolVersion.MINECRAFT_1_9) >= 0) {
-      buf.writeBoolean(assumeCommand);
-    }
-    buf.writeBoolean(hasPosition);
-    if (hasPosition) {
-      buf.writeLong(position);
+
+    if (version.compareTo(MINECRAFT_1_13) >= 0) {
+      ProtocolUtils.writeVarInt(buf, transactionId);
+      ProtocolUtils.writeString(buf, command);
+    } else {
+      ProtocolUtils.writeString(buf, command);
+      if (version.compareTo(MINECRAFT_1_9) >= 0) {
+        buf.writeBoolean(assumeCommand);
+      }
+      buf.writeBoolean(hasPosition);
+      if (hasPosition) {
+        buf.writeLong(position);
+      }
     }
   }
 

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/TabCompleteResponse.java

@@ -1,5 +1,8 @@
 package com.velocitypowered.proxy.protocol.packet;
 
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_13;
+
+import com.google.common.base.MoreObjects;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
@@ -7,35 +10,95 @@ import com.velocitypowered.proxy.protocol.ProtocolUtils;
 import io.netty.buffer.ByteBuf;
 import java.util.ArrayList;
 import java.util.List;
+import net.kyori.text.Component;
+import net.kyori.text.serializer.ComponentSerializers;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class TabCompleteResponse implements MinecraftPacket {
 
-  private final List<String> offers = new ArrayList<>();
+  private int transactionId;
+  private int start;
+  private int length;
+  private final List<Offer> offers = new ArrayList<>();
 
-  public List<String> getOffers() {
+  public int getTransactionId() {
+    return transactionId;
+  }
+
+  public void setTransactionId(int transactionId) {
+    this.transactionId = transactionId;
+  }
+
+  public int getStart() {
+    return start;
+  }
+
+  public void setStart(int start) {
+    this.start = start;
+  }
+
+  public int getLength() {
+    return length;
+  }
+
+  public void setLength(int length) {
+    this.length = length;
+  }
+
+  public List<Offer> getOffers() {
     return offers;
   }
 
   @Override
   public String toString() {
     return "TabCompleteResponse{"
-        + "offers=" + offers
+        + "transactionId=" + transactionId
+        + ", start=" + start
+        + ", length=" + length
+        + ", offers=" + offers
         + '}';
   }
 
   @Override
   public void decode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion version) {
-    int offersAvailable = ProtocolUtils.readVarInt(buf);
-    for (int i = 0; i < offersAvailable; i++) {
-      offers.add(ProtocolUtils.readString(buf));
+    if (version.compareTo(MINECRAFT_1_13) >= 0) {
+      this.transactionId = ProtocolUtils.readVarInt(buf);
+      this.start = ProtocolUtils.readVarInt(buf);
+      this.length = ProtocolUtils.readVarInt(buf);
+      int offersAvailable = ProtocolUtils.readVarInt(buf);
+      for (int i = 0; i < offersAvailable; i++) {
+        String offer = ProtocolUtils.readString(buf);
+        Component tooltip = buf.readBoolean() ? ComponentSerializers.JSON.deserialize(
+            ProtocolUtils.readString(buf)) : null;
+        offers.add(new Offer(offer, tooltip));
+      }
+    } else {
+      int offersAvailable = ProtocolUtils.readVarInt(buf);
+      for (int i = 0; i < offersAvailable; i++) {
+        offers.add(new Offer(ProtocolUtils.readString(buf), null));
+      }
     }
   }
 
   @Override
   public void encode(ByteBuf buf, ProtocolUtils.Direction direction, ProtocolVersion version) {
-    ProtocolUtils.writeVarInt(buf, offers.size());
-    for (String offer : offers) {
-      ProtocolUtils.writeString(buf, offer);
+    if (version.compareTo(MINECRAFT_1_13) >= 0) {
+      ProtocolUtils.writeVarInt(buf, this.transactionId);
+      ProtocolUtils.writeVarInt(buf, this.start);
+      ProtocolUtils.writeVarInt(buf, this.length);
+      ProtocolUtils.writeVarInt(buf, offers.size());
+      for (Offer offer : offers) {
+        ProtocolUtils.writeString(buf, offer.text);
+        buf.writeBoolean(offer.tooltip != null);
+        if (offer.tooltip != null) {
+          ProtocolUtils.writeString(buf, ComponentSerializers.JSON.serialize(offer.tooltip));
+        }
+      }
+    } else {
+      ProtocolUtils.writeVarInt(buf, offers.size());
+      for (Offer offer : offers) {
+        ProtocolUtils.writeString(buf, offer.text);
+      }
     }
   }
 
@@ -43,4 +106,29 @@ public class TabCompleteResponse implements MinecraftPacket {
   public boolean handle(MinecraftSessionHandler handler) {
     return handler.handle(this);
   }
+
+  public static class Offer implements Comparable<Offer> {
+    private final String text;
+    @Nullable
+    private final Component tooltip;
+
+    public Offer(String text,
+        @Nullable Component tooltip) {
+      this.text = text;
+      this.tooltip = tooltip;
+    }
+
+    @Override
+    public String toString() {
+      return MoreObjects.toStringHelper(this)
+          .add("text", text)
+          .add("tooltip", tooltip)
+          .toString();
+    }
+
+    @Override
+    public int compareTo(Offer o) {
+      return this.text.compareTo(o.text);
+    }
+  }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/ArgumentPropertyRegistry.java

@@ -0,0 +1,122 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import static com.velocitypowered.proxy.protocol.packet.brigadier.DoubleArgumentPropertySerializer.DOUBLE;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.DummyVoidArgumentPropertySerializer.DUMMY;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.FloatArgumentPropertySerializer.FLOAT;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.INTEGER;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.StringArgumentPropertySerializer.STRING;
+
+import com.mojang.brigadier.arguments.ArgumentType;
+import com.mojang.brigadier.arguments.BoolArgumentType;
+import com.mojang.brigadier.arguments.DoubleArgumentType;
+import com.mojang.brigadier.arguments.FloatArgumentType;
+import com.mojang.brigadier.arguments.IntegerArgumentType;
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.velocitypowered.proxy.protocol.ProtocolUtils;
+import io.netty.buffer.ByteBuf;
+import java.util.HashMap;
+import java.util.Map;
+
+public class ArgumentPropertyRegistry {
+  private ArgumentPropertyRegistry() {
+    throw new AssertionError();
+  }
+
+  private static final Map<String, ArgumentPropertySerializer<?>> byId = new HashMap<>();
+  private static final Map<Class<? extends ArgumentType>,
+      ArgumentPropertySerializer<?>> byClass = new HashMap<>();
+  private static final Map<Class<? extends ArgumentType>, String> classToId = new HashMap<>();
+
+  private static <T extends ArgumentType<?>> void register(String identifier, Class<T> klazz,
+      ArgumentPropertySerializer<T> serializer) {
+    byId.put(identifier, serializer);
+    byClass.put(klazz, serializer);
+    classToId.put(klazz, identifier);
+  }
+
+  private static <T> void dummy(String identifier, ArgumentPropertySerializer<T> serializer) {
+    byId.put(identifier, serializer);
+  }
+
+  public static ArgumentType<?> deserialize(ByteBuf buf) {
+    String identifier = ProtocolUtils.readString(buf);
+    ArgumentPropertySerializer<?> serializer = byId.get(identifier);
+    if (serializer == null) {
+      throw new IllegalArgumentException("Argument type identifier " + identifier + " unknown.");
+    }
+    Object result = serializer.deserialize(buf);
+
+    if (result instanceof ArgumentType) {
+      return (ArgumentType<?>) result;
+    } else {
+      return new DummyProperty(identifier, serializer, result);
+    }
+  }
+
+  public static void serialize(ByteBuf buf, ArgumentType<?> type) {
+    if (type instanceof DummyProperty) {
+      DummyProperty property = (DummyProperty) type;
+      ProtocolUtils.writeString(buf, property.getIdentifier());
+      if (property.getResult() != null) {
+        property.getSerializer().serialize(property.getResult(), buf);
+      }
+    } else {
+      ArgumentPropertySerializer serializer = byClass.get(type.getClass());
+      String id = classToId.get(type.getClass());
+      if (serializer == null || id == null) {
+        throw new IllegalArgumentException("Don't know how to serialize "
+            + type.getClass().getName());
+      }
+      ProtocolUtils.writeString(buf, id);
+      serializer.serialize(type, buf);
+    }
+  }
+
+  static {
+    // Base Brigadier argument types
+    register("brigadier:string", StringArgumentType.class, STRING);
+    register("brigadier:integer", IntegerArgumentType.class, INTEGER);
+    register("brigadier:float", FloatArgumentType.class, FLOAT);
+    register("brigadier:double", DoubleArgumentType.class, DOUBLE);
+    register("brigadier:bool", BoolArgumentType.class,
+        VoidArgumentPropertySerializer.create(BoolArgumentType::bool));
+
+    // Minecraft argument types with extra properties
+    dummy("minecraft:entity", ByteArgumentPropertySerializer.BYTE);
+    dummy("minecraft:score_holder", ByteArgumentPropertySerializer.BYTE);
+
+    // Minecraft argument types
+    dummy("minecraft:game_profile", DUMMY);
+    dummy("minecraft:block_pos", DUMMY);
+    dummy("minecraft:column_pos", DUMMY);
+    dummy("minecraft:vec3", DUMMY);
+    dummy("minecraft:vec2", DUMMY);
+    dummy("minecraft:block_state", DUMMY);
+    dummy("minecraft:block_predicate", DUMMY);
+    dummy("minecraft:item_stack", DUMMY);
+    dummy("minecraft:item_predicate", DUMMY);
+    dummy("minecraft:color", DUMMY);
+    dummy("minecraft:component", DUMMY);
+    dummy("minecraft:message", DUMMY);
+    dummy("minecraft:nbt", DUMMY);
+    dummy("minecraft:nbt_path", DUMMY);
+    dummy("minecraft:objective", DUMMY);
+    dummy("minecraft:objective_criteria", DUMMY);
+    dummy("minecraft:operation", DUMMY);
+    dummy("minecraft:particle", DUMMY);
+    dummy("minecraft:rotation", DUMMY);
+    dummy("minecraft:scoreboard_slot", DUMMY);
+    dummy("minecraft:swizzle", DUMMY);
+    dummy("minecraft:team", DUMMY);
+    dummy("minecraft:item_slot", DUMMY);
+    dummy("minecraft:resource_location", DUMMY);
+    dummy("minecraft:mob_effect", DUMMY);
+    dummy("minecraft:function", DUMMY);
+    dummy("minecraft:entity_anchor", DUMMY);
+    dummy("minecraft:item_enchantment", DUMMY);
+    dummy("minecraft:entity_summon", DUMMY);
+    dummy("minecraft:dimension", DUMMY);
+    dummy("minecraft:int_range", DUMMY);
+    dummy("minecraft:float_range", DUMMY);
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/ArgumentPropertySerializer.java

@@ -0,0 +1,10 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public interface ArgumentPropertySerializer<T> {
+  @Nullable T deserialize(ByteBuf buf);
+
+  void serialize(T object, ByteBuf buf);
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/ByteArgumentPropertySerializer.java

@@ -0,0 +1,24 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class ByteArgumentPropertySerializer implements ArgumentPropertySerializer<Byte> {
+
+  static final ByteArgumentPropertySerializer BYTE = new ByteArgumentPropertySerializer();
+
+  private ByteArgumentPropertySerializer() {
+
+  }
+
+  @Nullable
+  @Override
+  public Byte deserialize(ByteBuf buf) {
+    return buf.readByte();
+  }
+
+  @Override
+  public void serialize(Byte object, ByteBuf buf) {
+    buf.writeByte(object);
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/DoubleArgumentPropertySerializer.java

@@ -0,0 +1,41 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.HAS_MAXIMUM;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.HAS_MINIMUM;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.getFlags;
+
+import com.mojang.brigadier.arguments.DoubleArgumentType;
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class DoubleArgumentPropertySerializer implements ArgumentPropertySerializer<DoubleArgumentType> {
+
+  static final DoubleArgumentPropertySerializer DOUBLE = new DoubleArgumentPropertySerializer();
+
+  private DoubleArgumentPropertySerializer() {
+  }
+
+  @Nullable
+  @Override
+  public DoubleArgumentType deserialize(ByteBuf buf) {
+    byte flags = buf.readByte();
+    double minimum = (flags & HAS_MINIMUM) != 0 ? buf.readDouble() : Double.MIN_VALUE;
+    double maximum = (flags & HAS_MAXIMUM) != 0 ? buf.readDouble() : Double.MAX_VALUE;
+    return DoubleArgumentType.doubleArg(minimum, maximum);
+  }
+
+  @Override
+  public void serialize(DoubleArgumentType object, ByteBuf buf) {
+    boolean hasMinimum = object.getMinimum() != Double.MIN_VALUE;
+    boolean hasMaximum = object.getMaximum() != Double.MAX_VALUE;
+    byte flag = getFlags(hasMinimum, hasMaximum);
+
+    buf.writeByte(flag);
+    if (hasMinimum) {
+      buf.writeDouble(object.getMinimum());
+    }
+    if (hasMaximum) {
+      buf.writeDouble(object.getMaximum());
+    }
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/DummyProperty.java

@@ -0,0 +1,37 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import com.mojang.brigadier.StringReader;
+import com.mojang.brigadier.arguments.ArgumentType;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class DummyProperty<T> implements ArgumentType<T> {
+
+  private final String identifier;
+  private final ArgumentPropertySerializer<T> serializer;
+  @Nullable
+  private final T result;
+
+  DummyProperty(String identifier, ArgumentPropertySerializer<T> serializer, @Nullable T result) {
+    this.identifier = identifier;
+    this.serializer = serializer;
+    this.result = result;
+  }
+
+  @Override
+  public <S> T parse(StringReader reader) throws CommandSyntaxException {
+    throw new UnsupportedOperationException();
+  }
+
+  public String getIdentifier() {
+    return identifier;
+  }
+
+  public ArgumentPropertySerializer<T> getSerializer() {
+    return serializer;
+  }
+
+  public @Nullable T getResult() {
+    return result;
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/DummyVoidArgumentPropertySerializer.java

@@ -0,0 +1,27 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * An argument property serializer that will serialize and deserialize nothing.
+ */
+class DummyVoidArgumentPropertySerializer implements ArgumentPropertySerializer<Void> {
+
+  static final ArgumentPropertySerializer<Void> DUMMY =
+      new DummyVoidArgumentPropertySerializer();
+
+  private DummyVoidArgumentPropertySerializer() {
+  }
+
+  @Nullable
+  @Override
+  public Void deserialize(ByteBuf buf) {
+    return null;
+  }
+
+  @Override
+  public void serialize(Void object, ByteBuf buf) {
+
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/FloatArgumentPropertySerializer.java

@@ -0,0 +1,42 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.HAS_MAXIMUM;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.HAS_MINIMUM;
+import static com.velocitypowered.proxy.protocol.packet.brigadier.IntegerArgumentPropertySerializer.getFlags;
+
+import com.mojang.brigadier.arguments.FloatArgumentType;
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class FloatArgumentPropertySerializer implements ArgumentPropertySerializer<FloatArgumentType> {
+
+  static FloatArgumentPropertySerializer FLOAT = new FloatArgumentPropertySerializer();
+
+  private FloatArgumentPropertySerializer() {
+
+  }
+
+  @Nullable
+  @Override
+  public FloatArgumentType deserialize(ByteBuf buf) {
+    byte flags = buf.readByte();
+    float minimum = (flags & HAS_MINIMUM) != 0 ? buf.readFloat() : Float.MIN_VALUE;
+    float maximum = (flags & HAS_MAXIMUM) != 0 ? buf.readFloat() : Float.MAX_VALUE;
+    return FloatArgumentType.floatArg(minimum, maximum);
+  }
+
+  @Override
+  public void serialize(FloatArgumentType object, ByteBuf buf) {
+    boolean hasMinimum = object.getMinimum() != Float.MIN_VALUE;
+    boolean hasMaximum = object.getMaximum() != Float.MAX_VALUE;
+    byte flag = getFlags(hasMinimum, hasMaximum);
+
+    buf.writeByte(flag);
+    if (hasMinimum) {
+      buf.writeFloat(object.getMinimum());
+    }
+    if (hasMaximum) {
+      buf.writeFloat(object.getMaximum());
+    }
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/IntegerArgumentPropertySerializer.java

@@ -0,0 +1,52 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import com.mojang.brigadier.arguments.IntegerArgumentType;
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class IntegerArgumentPropertySerializer implements ArgumentPropertySerializer<IntegerArgumentType> {
+
+  static final IntegerArgumentPropertySerializer INTEGER = new IntegerArgumentPropertySerializer();
+
+  static final byte HAS_MINIMUM = 0x01;
+  static final byte HAS_MAXIMUM = 0x02;
+
+  private IntegerArgumentPropertySerializer() {
+
+  }
+
+  @Nullable
+  @Override
+  public IntegerArgumentType deserialize(ByteBuf buf) {
+    byte flags = buf.readByte();
+    int minimum = (flags & HAS_MINIMUM) != 0 ? buf.readInt() : Integer.MIN_VALUE;
+    int maximum = (flags & HAS_MAXIMUM) != 0 ? buf.readInt() : Integer.MAX_VALUE;
+    return IntegerArgumentType.integer(minimum, maximum);
+  }
+
+  @Override
+  public void serialize(IntegerArgumentType object, ByteBuf buf) {
+    boolean hasMinimum = object.getMinimum() != Integer.MIN_VALUE;
+    boolean hasMaximum = object.getMaximum() != Integer.MAX_VALUE;
+    byte flag = getFlags(hasMinimum, hasMaximum);
+
+    buf.writeByte(flag);
+    if (hasMinimum) {
+      buf.writeInt(object.getMinimum());
+    }
+    if (hasMaximum) {
+      buf.writeInt(object.getMaximum());
+    }
+  }
+
+  static byte getFlags(boolean hasMinimum, boolean hasMaximum) {
+    byte flags = 0;
+    if (hasMinimum) {
+      flags |= HAS_MINIMUM;
+    }
+    if (hasMaximum) {
+      flags |= HAS_MAXIMUM;
+    }
+    return flags;
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/StringArgumentPropertySerializer.java

@@ -0,0 +1,52 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import com.mojang.brigadier.arguments.StringArgumentType;
+import com.velocitypowered.proxy.protocol.ProtocolUtils;
+import io.netty.buffer.ByteBuf;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * Serializes properties for {@link StringArgumentType}.
+ */
+class StringArgumentPropertySerializer implements ArgumentPropertySerializer<StringArgumentType> {
+
+  public static final ArgumentPropertySerializer<StringArgumentType> STRING =
+      new StringArgumentPropertySerializer();
+
+  private StringArgumentPropertySerializer() {
+
+  }
+
+  @Nullable
+  @Override
+  public StringArgumentType deserialize(ByteBuf buf) {
+    int type = ProtocolUtils.readVarInt(buf);
+    switch (type) {
+      case 0:
+        return StringArgumentType.word();
+      case 1:
+        return StringArgumentType.string();
+      case 2:
+        return StringArgumentType.greedyString();
+      default:
+        throw new IllegalArgumentException("Invalid string argument type " + type);
+    }
+  }
+
+  @Override
+  public void serialize(StringArgumentType object, ByteBuf buf) {
+    switch (object.getType()) {
+      case SINGLE_WORD:
+        ProtocolUtils.writeVarInt(buf, 0);
+        break;
+      case QUOTABLE_PHRASE:
+        ProtocolUtils.writeVarInt(buf, 1);
+        break;
+      case GREEDY_PHRASE:
+        ProtocolUtils.writeVarInt(buf, 2);
+        break;
+      default:
+        throw new IllegalArgumentException("Invalid string argument type " + object.getType());
+    }
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/brigadier/VoidArgumentPropertySerializer.java

@@ -0,0 +1,32 @@
+package com.velocitypowered.proxy.protocol.packet.brigadier;
+
+import com.mojang.brigadier.arguments.ArgumentType;
+import io.netty.buffer.ByteBuf;
+import java.util.function.Supplier;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+class VoidArgumentPropertySerializer<T extends ArgumentType<?>>
+    implements ArgumentPropertySerializer<T> {
+
+  private final Supplier<T> argumentSupplier;
+
+  public VoidArgumentPropertySerializer(Supplier<T> argumentSupplier) {
+    this.argumentSupplier = argumentSupplier;
+  }
+
+  public static <T extends ArgumentType<?>> ArgumentPropertySerializer<T> create(
+      Supplier<T> supplier) {
+    return new VoidArgumentPropertySerializer<T>(supplier);
+  }
+
+  @Nullable
+  @Override
+  public T deserialize(ByteBuf buf) {
+    return argumentSupplier.get();
+  }
+
+  @Override
+  public void serialize(T object, ByteBuf buf) {
+
+  }
+}